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Clamping Inconel parts to a fixture with tailstock pressure.

Bulletsnatch

Plastic
Joined
Feb 20, 2021
Hello all. I'm making some parts out of 718 that come to me as .625" x 3.600" bar with a .350" hole gun drilled through the center. First op machines a tube port with an OD of .565", an ID of .450", and a depth of .360". Second op clamps on that port with a collet and uses the tailstock and a little plug in the gun drilled hole to fit the tailstock. Then turns the rest of the OD to .450". So it basically becomes a little tube with a port at one end. When I clamp on the port with my minimum 100# pressure it crushes it by about a thou. My boss said to make a fixture for it and clamp on that. I made two plugs out of 718 to fit in the ID at .450" x .300" with a couple tenths in between the part and the plug. And then turned a shoulder up to .625" to clamp on with my collet. Using tailstock pressure to clamp the part to the shoulder of the plug I showed my boss and he said no. Nixed all my work and had me make pins to fit in the port so when I clamp on it they don't let it crush. I told him they would just get stuck in the port. Even though we're going his way I was curious if my idea would work. If I pressed the part against the plug I'm clamping on with 100#-200# of tailstock pressure and tried to turn it with light passes would it spin on my fixture or would it work?
 

SeymourDumore

Diamond
Joined
Aug 2, 2005
Location
CT
If I pressed the part against the plug I'm clamping on with 100#-200# of tailstock pressure and tried to turn it with light passes would it spin on my fixture or would it work?

Probably not, but even if it didn't spin you would have a hard time holding any tolerance on the OD with only a .05 wall for some unsupported 3" length.
But to make you feel better, I think your boss's idea would fail as well.

However ...
If you make a plug that supports the part for the whole 3.6" length ( port dia on the chuck side and then perhaps .348-.346 for the length of the part, then you will have a chance.
To make it even better and even less likely to spin, force some "direct drive" into your tailstock.
As-is, friction between your plug and the part is the only thing that drives the part AND the tailstock.
But, if the plug is made of 2 pieces and you put a drive pin ( an offset 1/8 dowel will do fine ) between the chuck-side plug and the tailstock-side plug, then the tailstock only has to
create enough force to drive the part because the plug will drive the tailstock by itself.

......

(Reading back I am not sure if I made myself clear ... :scratchchin:)
 

Delw

Stainless
Joined
Jan 8, 2019
your only getting 100LBS min? thats odd.
you should be able to adjust the pressure down to Zero all you need to do is make the collet open and close.
 

Bulletsnatch

Plastic
Joined
Feb 20, 2021
And seymore that would be worth a shot if the gun drilled hole wasn't running out .010"-.015" on some parts. Which it's just another nightmare I get to work around today
 

SeymourDumore

Diamond
Joined
Aug 2, 2005
Location
CT
Actually that can easily be remedied, though it is an extra OP.
But then again .010 over 3.5" long on a .350 dia?
My guy hits a 5" long TI with .063 through within .003!
Not cheap, but worth it.
 








 
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